The spine is formed of superposed vertebrae, normally aligned along a vertebral axis from the lumbar vertebrae to the cervical vertebrae, each having a posterior wall from which projects a spinous process and two lateral edges from the walls of which project ribs and/or transverse process. Each vertebra also has two lateral pedicles and lamina surfaces. Accompanying FIG. 1 shows vertebrae V and V′ with the different parts thereof. Reference TP designates the transversal processes, reference P designates the pedicles of the vertebra and reference L designates the lamina.
In order to straighten or stabilize the vertebrae of a spine it is well known to use a stabilizing system which includes a longitudinal connecting rod and several fixing elements. Each fixing element is secured to one of the vertebrae to be stabilized and the connecting rod is secured to each fixing element, so that portions of the connecting rod are secured to the vertebrae to be stabilized. The fixing elements include a head to be secured to the rod and a fixing member which may consist of a screw (for example a pedicle screw) or a hook. When the patient who is equipped with such a stabilizing system moves his spine, forces are developed by the fixing members of the fixing elements in the vertebrae. In particular, the fixing elements disposed at the extremities of the rod of the stabilizing system or spinal construction assembly, develop the greatest forces. It is therefore apparent that it would be advantageous to try to decrease the forces developed at the extremities of the spinal construction assembly.
For this purpose, an orthopaedic device has been previously proposed in International Patent Application WO 2010/043496 A1, comprising a first rod with a ball-shaped first end, and a connecting element. The connecting element comprises an anchor for securing said connecting element to a bone, in particular a vertebra, a socket for receiving said ball-shaped first end of the first rod so as to form a ball-and-socket joint, a first lateral opening, and a top opening with a first inner screw thread wherein a lock screw is received for locking, within said socket, said ball-shaped first end of the first rod. By “locking”, in the context of the present disclosure, it is meant blocking the position of two parts with respect to each other, and only eventually also their orientation.
During the assembly of this prior art orthopaedic device, the ball-shaped first end of the first rod is introduced into the socket through the top opening of the connecting element. The lock screw can thus be threaded into the top opening only after the introduction of the ball-shaped rod end, and thus, when the connecting element is anchored to a bone, in the middle of the surgery operation, increasing the surgical staff's workload.